<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>isWeekend</title>
</head>
<body>
    <script>
        const isWeekend = (d = new Date()) => d.getDay() % 6 === 0;
        document.writeln(`今天${ isWeekend() ? '' : '不' }是周末!`);
    </script>
</body>
</html>